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Algae samples raise concern in St. Johns River

Blue green algae is shown last year in the St. Johns River.
Edie Widder
St. Johns Riverkeeper
Blue green algae in the St. Johns River.

Test results from algae samples recently collected by St. Johns Riverkeeper found toxin levels up to 300 times the recreational safe limit for microcystins.

The Environmental Protection Agency’s recommended limit for recreational water quality or swimming advisories is 8 micrograms per liter — or ug/L — total microcystins.

All five samples tested by Greenwater Labs contained toxins far in excess of what is considered safe for swimming and recreation. The samples were collected at these locations on Sept. 27 and 28:

  • St. Johns River at St. Vincent's Hospital, 1,060 ug/L.
  • St. Johns at the end of Seminole Road in Avondale. 2,415 ug/L
  • Trout River near Highway 17/Main Street Bridge, 54.8 ug/L.
  • St. Johns River at River Road in San Marco (9/28/21) 615 ug/L.
  • · Mouth of Craig Creek in San Marco, 491 ug/L.

The St. Johns Riverkeeper test results differ dramatically from samples recently taken by the Florida Department of Environmental Protection at similar locations:

  • St. Johns River at St. Vincent's Hospital, 3.9 ug/L.
  • St. Johns – Canal to Marco Lake in San Marco, 24 ug/L.
  • Mouth of Craig Creek, 1.5 ug/L.

“Our sample results demonstrate how toxic some of these algae blooms can be,” said Lisa Rinaman. “Unfortunately, there is no way to determine if a bloom is toxic without testing, so it is best to avoid contact and exposure with all algae outbreaks you may encounter.”

Toxins produced by the blooms can cause rashes, stomach cramps, nausea, diarrhea and respiratory irritation. High exposure to toxins can affect the liver and nervous system.

If skin contact occurs, wash off immediately and thoroughly with clean water and soap. Long-term exposure can potentially result in nerve or liver damage. These toxins can be dangerous depending on concentration levels and pathways of exposure.

Pet owners should prevent their pets from drinking or swimming in bodies of water where algal blooms are present. Ingestion of algal toxins can cause an animal to become extremely ill. If contact occurs, rinse off immediately and keep them from licking their fur.

While blue-green algae, also known as cyanobacteria, is naturally present in our waterways, excessive nutrients from fertilizers, manure, industrial wastewater and failing septic tanks can stimulate the growth of toxic algae blooms.

Algae blooms block sunlight from reaching submerged aquatic plants and clog fish gills. As blooms die and decompose, oxygen levels are depleted causing fish kills. They can also produce harmful toxins.

Citizens can help prevent algae blooms and nutrient pollution by limiting the use of fertilizers, picking up dog waste, maintaining septic tanks and reaching out to their elected officials to demand protective policies to reduce nutrient loading in our waterways.

If citizens spot what looks like bright green, paint-like scum on the surface of the water, they should steer clear. Do not recreate, boat, swim or fish near an algae bloom.

If you encounter an algae bloom, report it to the Florida Department of Environmental Protection by calling 855-305-3903 or completing an online form. You can also report to St. Johns RIVERKEEPER at